JP2019131679A - Adhesive sheet and production method of the same, and method for manufacturing image display device - Google Patents

Abstract

To provide an adhesive sheet having a step absorbing property and excellent shock resistance in a wide temperature range and adhesion durability against a strain stress.SOLUTION: An adhesive sheet (5) is a photo-curable adhesive sheet, formed in a layer state from an adhesive composition comprising a base polymer and a photocurable compound. The adhesive sheet (5) has a haze of 1% or less, an adhesion force of 1.5 N/10 mm or more with respect to glass, and a shear storage modulus of 0.15 MPa or less at 25°C. When a polymerization rate of the adhesive sheet (5) by curing is controlled to 99%, the sheet shows a glass transition temperature of -3°C or lower and a shear storage modulus of 0.16 MPa or more at 25°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pressure-sensitive adhesive sheet and a method for producing the same. Furthermore, this invention relates to the manufacturing method of the image display apparatus using the said adhesive sheet.

  Liquid crystal display devices and organic EL display devices are widely used as various image display devices such as mobile phones, smart phones, car navigation devices, personal computer monitors, and televisions. For the purpose of preventing damage to the image display panel due to impact from the outer surface, a front transparent plate (also referred to as “cover window” or the like) such as a transparent resin plate or a glass plate is provided on the viewing side of the image display panel. Sometimes. In recent years, devices having a touch panel on the viewing side of an image display panel have become widespread.

  As a method of disposing a front transparent member such as a front transparent plate or a touch panel on the front surface of the image display panel, an “interlayer filling structure” in which the image display panel and the front transparent member are bonded via an adhesive sheet has been proposed. An adhesive sheet may also be provided between the touch panel and the front transparent plate. In the interlayer filling structure, since the gap between the members is filled with the adhesive, the difference in the refractive index at the interface is reduced, and the reduction in visibility due to reflection and scattering is suppressed. Moreover, in the interlayer filling structure, since the members are bonded and fixed by the adhesive sheet, the front transparent member is peeled off due to an impact such as dropping as compared with the case where the front transparent member is fixed only to the housing. There is an advantage with difficulty.

  A colored layer (decorative printing layer) for the purpose of decoration or light shielding may be formed on the periphery of the front transparent member. When an adhesive is bonded to a transparent member having a decorative print layer, bubbles are likely to be generated around the printing step portion. By providing a step absorbability using a thick adhesive sheet, it is possible to suppress problems such as air bubble mixing. Moreover, there exists a tendency for impact resistance to improve by using a thick adhesive sheet.

  Since a thick adhesive sheet can be formed with a uniform thickness, a solvent-free photo-curing adhesive is widely used for an interlayer filling adhesive sheet (for example, Patent Document 1 and Patent Document 2). reference). In the case of using a photocurable pressure-sensitive adhesive, photocuring can also be performed after bonding a pressure-sensitive adhesive sheet in which a part of the pressure-sensitive adhesive composition is uncured (semi-cured) to an adherend. In this method, since the semi-cured pressure-sensitive adhesive sheet has high fluidity, the step absorbability at the time of bonding is high, and the adhesive holding power can be improved by subsequent photocuring.

JP 2014-125524 A International Publication No. 2013/161666

  Conventionally, the front transparent member such as a cover window has a size larger than that of the display panel, and the front transparent member and the housing are bonded together with an adhesive tape or the like in a region outside the outer peripheral edge of the display panel. That is, the front transparent member has been fixed by a combination of bonding to the housing and bonding to the display panel surface by the interlayer filling adhesive sheet.

  In recent years, narrowing of the frame and bezel-less display devices are progressing mainly in mobile devices such as smartphones. As the frame is narrowed or bezelless, the size of the display panel 10 is equal to or larger than the size of the front transparent member 7. In such a configuration, the housing 9 and the front transparent member 7 cannot be fixed with an adhesive tape or the like, and it is necessary to fix the front transparent member 7 only with the adhesive sheet 5 for interlayer filling (see FIG. 2). ). Along with this, the pressure-sensitive adhesive sheet for interlayer filling is required to have higher adhesive force and not to be peeled off by impact such as dropping in a wide temperature range.

  Further, when the size of the display panel is equal to or larger than the size of the front transparent member, sealing with a resin material is used to fill the gap 90 between the housing 9 and the front transparent member 7. It may be done. For example, after a molten resin material is poured into the gap 90, the resin material is solidified by cooling to room temperature, thereby sealing with the resin material. When high temperature resin is poured into the gap 90, the front transparent member 7, the housing 9 and the adhesive sheet 5 become high in the vicinity of the gap 90, and are cooled when the resin is solidified. The adhesive sheet 5 has an adhesive durability against strain stress so that peeling between the adherends does not occur even when dimensional distortion occurs in the front transparent member and the housing due to such a temperature change. Is required.

  Since the conventional interlayer filling pressure-sensitive adhesive sheet disclosed in Patent Document 1 has a high glass transition temperature, it has poor adhesion and impact resistance at low temperatures. On the other hand, the low glass temperature adhesive sheet disclosed in Patent Document 2 has low adhesion durability against strain stress, low temperature impact resistance, and durability against strain stress during heating / cooling such as resin sealing. It is difficult to balance the sex.

  In view of the above, an object of the present invention is to provide a pressure-sensitive adhesive sheet that has step absorbability and is excellent in impact resistance in a wide temperature range and adhesion durability against strain stress.

  The present invention relates to a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive containing a base polymer is formed into a sheet shape. The haze of the pressure-sensitive adhesive sheet is 1% or less.

  In one embodiment, the pressure-sensitive adhesive sheet is a photo-curable pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive composition containing a base polymer and a photocurable compound is formed in a layer shape. The photocurable pressure-sensitive adhesive sheet has an adhesive strength to glass of 1.5 N / 10 mm or more and a shear storage elastic modulus at a temperature of 25 ° C. of 0.15 MPa or less.

  The photocurable pressure-sensitive adhesive composition is in a so-called semi-cured state and preferably has a polymerization rate of 90 to 98%. The glass transition temperature of the semi-cured adhesive sheet is preferably −5 ° C. or lower. The peak top value of the loss tangent of the semi-cured adhesive sheet is preferably 1.6 or more.

  In one embodiment of the pressure-sensitive adhesive sheet of the present invention, the polymerization rate of the pressure-sensitive adhesive composition is about 99% or more. Such a completely cured pressure-sensitive adhesive sheet can be obtained, for example, by photocuring the above-mentioned semi-cured pressure-sensitive adhesive sheet. A fully cured pressure sensitive adhesive sheet can also be obtained by photocuring a photocurable pressure sensitive adhesive sheet having a polymerization rate of less than 90%.

The glass transition temperature of the fully cured pressure-sensitive adhesive sheet is preferably −3 ° C. or lower. The shear storage modulus G ′ at _{25 °} C. of the fully cured pressure-sensitive adhesive sheet is preferably 0.16 MPa or more. The peak top value of the loss tangent of the fully cured pressure-sensitive adhesive sheet is preferably 1.5 or more. The semi-cured pressure-sensitive adhesive sheet preferably has a glass transition temperature and G ′ of _{25 ° C.} in the above range when the polymerization rate is increased to 99% by curing, and a peak top value of loss tangent is in the above range. Is preferred.

  As the base polymer contained in the pressure-sensitive adhesive sheet, for example, a polymer obtained by crosslinking an acrylic polymer chain with a urethane segment is used. In order to satisfy the above properties, the urethane segment content relative to 100 parts by weight of the acrylic polymer chain is preferably 3 to 30 parts by weight. As for the weight average molecular weight of a urethane type segment, 4000-50000 are preferable.

  A base polymer in which an acrylic polymer chain is cross-linked by a urethane segment is, for example, a copolymer of a monomer component constituting an acrylic polymer chain and a urethane (meth) acrylate having a (meth) acryloyl group at at least two ends. Is obtained. As the polyfunctional urethane (meth) acrylate, urethane di (meth) acrylate having (meth) acryloyl groups at both ends is preferable.

  The weight average molecular weight of urethane di (meth) acrylate is preferably 4000 to 50000. The glass transition temperature of urethane (meth) acrylate is preferably 0 ° C. or lower.

  The pressure-sensitive adhesive sheet containing a base polymer in which an acrylic polymer chain is cross-linked by a urethane-based segment is formed by laminating a composition containing an acrylic monomer and / or a partial polymer thereof and urethane di (meth) acrylate on a substrate. After coating, the composition is obtained by irradiating the composition with an actinic ray and performing photocuring. The pressure-sensitive adhesive composition preferably has a urethane (meth) acrylate content of 3 to 30 parts by weight based on 100 parts by weight of the acrylic monomer and its partial polymer.

  The pressure-sensitive adhesive sheet of the present invention is used, for example, for laminating a transparent member in an image display device in which the transparent member is arranged on the viewing side surface. When using a semi-cured adhesive sheet, the adhesive sheet and the transparent member are bonded together, and then the adhesive sheet is irradiated with actinic rays, whereby the adhesive sheet is photocured to form an image display device. .

  Since the pressure-sensitive adhesive sheet of the present invention has a low glass transition temperature after complete curing and a high shear storage modulus, it can satisfy both impact resistance such as dropping and adhesion durability against strain stress in a wide temperature range. is there. Moreover, since the shear storage elastic modulus is small in the semi-cured state, the step absorbability is excellent. An image display device in which a cover window or the like is bonded to the surface on the viewing side using the pressure-sensitive adhesive sheet of the present invention has excellent adhesion reliability, and can cope with a narrow frame or bezelless.

It is sectional drawing which shows the structural example of the adhesive sheet with a release film. It is sectional drawing which shows the structural example of an image display apparatus. It is sectional drawing which shows the laminated structural example of an optical film with an adhesive sheet. It is sectional drawing which shows the laminated structural example of an optical film with an adhesive sheet. It is a photograph which shows the mode of an interlayer adhesive test. It is an observation photograph of a sample in which streaky air bubbles are generated in an interlayer adhesion test. It is a schematic diagram which shows arrangement | positioning of the sample in an impact resistance test.

  FIG. 1 shows a pressure-sensitive adhesive sheet with a release film in which release films 1 and 2 are temporarily attached to both surfaces of the pressure-sensitive adhesive sheet 5. FIG. 2 is a cross-sectional view illustrating a configuration example of an image display device in which the front transparent plate 7 is fixed using an adhesive sheet.

[Physical properties of adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention is a sheet in which a pressure-sensitive adhesive is formed. The pressure-sensitive adhesive sheet is a transparent pressure-sensitive adhesive sheet having a haze of 1.0% or less.

In one embodiment, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive sheet is a photocurable pressure-sensitive adhesive containing a monomer or oligomer (photopolymerizable compound) having a photopolymerizable functional group. The polymerization rate of the photocurable pressure-sensitive adhesive sheet is preferably 90 to 98%. In other words, the photocurable pressure-sensitive adhesive sheet is in a semi-cured state and preferably contains 2 to 10% by weight of a photopolymerizable compound. The polymerization rate of the pressure-sensitive adhesive sheet is calculated from the weight before and after heating the pressure-sensitive adhesive sheet at 130 ° C. for 3 hours by the following formula. The polymerization rate of the prepolymer described later is also calculated by the same method.
Polymerization rate (%) = weight after drying / weight before drying × 100

From the viewpoint of giving the pressure-sensitive adhesive sheet step absorbability and preventing air bubbles from being mixed in the vicinity of the printed step, the shear storage modulus G ′ at _{25 °} C. of the semi-cured pressure-sensitive adhesive sheet is preferably 0.15 MPa or less. . On the other hand, from the viewpoint of moldability and handling properties of the pressure-sensitive adhesive sheet, the G ′ _{25 ° C.} of the semi-cured pressure-sensitive adhesive sheet is preferably 0.03 MPa or more, more preferably 0.05 MPa or more, and further preferably 0.07 MPa or more.

When photocuring (post-curing) is performed after the semi-cured adhesive sheet is bonded to the adherend, the polymerization rate increases due to the polymerization reaction of the photopolymerizable compound, and the shear storage elastic modulus of the adhesive sheet increases. The pressure-sensitive adhesive sheet after complete curing by post-curing (when the polymerization rate is 99% or more) preferably has a shear storage modulus G ′ at _{25 ° C.} of _{25 ° C.} of 0.16 MPa or more. By G _{'25 ° C.} of the adhesive sheet after complete curing is not less than 0.16 MPa, adhesion reliability is enhanced. From the viewpoint of increasing the adhesive reliability at high temperatures, the shear storage modulus G ′ at _{80 °} C. of the pressure-sensitive adhesive sheet after complete curing is preferably 0.11 MPa or more.

On the other hand, from the viewpoint of ensuring wettability by giving the adhesive sheet an appropriate viscosity, the G ′ _{25 ° C.} of the fully cured adhesive sheet is preferably 1 MPa or less, more preferably 0.5 MPa or less, and 0.4 MPa or less. Further preferred. From the same viewpoint, the G ′ _{80 ° C.} of the pressure-sensitive adhesive sheet after complete curing is preferably 0.6 MPa or less, more preferably 0.4 MPa or less, and further preferably 0.3 MPa or less.

  The glass transition temperature of the semi-cured pressure-sensitive adhesive sheet is preferably −5 ° C. or lower. The glass transition temperature of the semi-cured pressure-sensitive adhesive sheet is preferably −25 ° C. or higher, more preferably −20 ° C. or higher, and further preferably −18 ° C. or higher. The glass transition temperature of the pressure-sensitive adhesive sheet after complete curing is preferably −3 ° C. or lower. The glass transition temperature of the pressure-sensitive adhesive sheet after complete curing is preferably −20 ° C. or higher, more preferably −15 ° C. or higher, and further preferably −13 ° C. or higher. When the glass transition temperature is within the above range, the pressure-sensitive adhesive sheet has an appropriate viscosity even in a low temperature region, and thus tends to be excellent in impact resistance.

  The peak top value (that is, tan δ at the glass transition temperature) of the loss tangent tan δ of the semi-cured pressure-sensitive adhesive sheet is preferably 1.6 or more, more preferably 1.7 or more, and further preferably 1.8 or more. The peak top value of tan δ of the pressure-sensitive adhesive sheet after complete curing is preferably 1.5 or more, more preferably 1.6 or more, and still more preferably 1.7 or more. A pressure-sensitive adhesive sheet having a large peak top value of tan δ has a large viscous behavior and tends to have excellent impact resistance.

  The shear storage modulus G ′, glass transition temperature, and peak top value of tan δ of the pressure-sensitive adhesive sheet can be determined by measuring viscoelasticity at a frequency of 1 Hz. The glass transition temperature is a temperature at which tan δ is maximized (peak top temperature). tan δ is a ratio G ″ / G ′ between the storage elastic modulus G ′ and the loss elastic modulus G ″. The storage elastic modulus G ′ corresponds to a portion that is stored as elastic energy when the material is deformed, and is an index representing the degree of hardness. The larger the storage elastic modulus of the pressure-sensitive adhesive sheet, the higher the adhesion holding force and the tendency to suppress peeling due to strain. The loss elastic modulus G ″ corresponds to a loss energy portion that is dissipated due to internal friction or the like when the material is deformed, and represents the degree of viscosity. The larger the tan δ, the stronger the tendency of viscosity, and the deformation behavior becomes liquid. The resilience energy tends to be small.

  In both the semi-cured pressure-sensitive adhesive sheet and the pressure-sensitive adhesive sheet after complete curing, the upper limit of the peak top value of tan δ is not particularly limited, but is generally 3.0 or less. From the viewpoint of adhesion holding force, the peak top value of tan δ is preferably 2.7 or less, and more preferably 2.5 or less.

  The adhesive strength of the semi-cured pressure-sensitive adhesive sheet is preferably 3N / 10 mm or more, more preferably 4N / 10 mm or more, and even more preferably 5N / 10 mm or more. After the release film 2 (light release film) temporarily attached to one surface of the pressure-sensitive adhesive sheet 5 is peeled off and bonded to the adherend, the adhesive strength of the semi-cured pressure-sensitive adhesive sheet is in the above range, When peeling the release film 1 (heavy release film) temporarily attached to the other surface, peeling at the interface between the adherend and the pressure-sensitive adhesive sheet 5 can be suppressed.

  The adhesive strength of the pressure-sensitive adhesive sheet after complete curing is preferably 2N / 10 mm or more, more preferably 2.5 N / 10 mm or more, and further preferably 3 N / 10 mm or more. When the adhesive force of the pressure-sensitive adhesive sheet after complete curing is within the above range, it is possible to prevent the pressure-sensitive adhesive sheet from peeling off from the adherend when a stress due to strain or an impact due to dropping occurs.

  The adhesive force is determined by a peel test using a glass plate as an adherend and a tensile speed of 60 mm / min and a peel angle of 180 °. Unless otherwise specified, the adhesive strength is a value measured at 25 ° C.

  The adhesive strength at 65 ° C. of the semi-cured pressure-sensitive adhesive sheet at high temperature is preferably 1 N / 10 mm or more, more preferably 1.5 N / 10 mm or more, and further preferably 2 N / 10 mm or more. The adhesive strength at 65 ° C. of the pressure-sensitive adhesive sheet after complete curing is preferably 1 N / 10 mm or more, more preferably 1.5 N / 10 mm or more, and further preferably 2 N / 10 mm or more.

  The thickness of an adhesive sheet is not specifically limited, What is necessary is just to set with the kind, shape, etc. of a to-be-adhered body. When a member having a printing step such as a front transparent plate is used as the adherend, the thickness of the pressure-sensitive adhesive sheet is preferably larger than the thickness of the printing step. The thickness of the pressure-sensitive adhesive sheet used for pasting the front transparent plate (cover window) is preferably 30 μm or more, more preferably 40 μm or more, and further preferably 50 μm or more. By increasing the thickness of the pressure-sensitive adhesive sheet, the step absorbability and impact resistance tend to increase. The upper limit of the thickness of the pressure-sensitive adhesive sheet is not particularly limited, but is preferably 500 μm or less, more preferably 300 μm or less, and still more preferably 250 μm or less from the viewpoint of productivity of the pressure-sensitive adhesive sheet.

[Adhesive composition]
As long as the pressure-sensitive adhesive sheet of the present invention satisfies the above characteristics, the composition of the pressure-sensitive adhesive is not particularly limited, and is an acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate / vinyl chloride copolymer, Those having a base polymer of a polymer such as modified polyolefin, epoxy-based, fluorine-based, natural rubber, synthetic rubber or the like can be appropriately selected and used.

  In particular, acrylic adhesives that contain an acrylic polymer as a base polymer because of excellent optical transparency, adhesive properties such as moderate wettability, cohesiveness, and adhesiveness, and excellent weather resistance and heat resistance. An agent is preferably used. Among them, an acrylic base polymer having a structure in which an acrylic polymer chain is crosslinked by a urethane segment is preferable.

[Base polymer]
When the acrylic polymer chain is cross-linked by the urethane segment, a high adhesion holding force can be exhibited at a low glass transition temperature. The base polymer preferably has a urethane segment content of 3 parts by weight or more based on 100 parts by weight of the acrylic polymer chain.

  When the amount of the urethane segment is excessively large, the viscosity of the pressure-sensitive adhesive decreases with an increase in the crosslinking density, and the step absorbability and impact resistance may decrease. Moreover, when the quantity of a urethane-type segment becomes large too much, the transparency of an adhesive sheet may fall and a haze may raise. Therefore, the amount of the urethane segment in the base polymer is preferably 30 parts by weight or less and more preferably 25 parts by weight or less with respect to 100 parts by weight of the acrylic polymer chain.

<Acrylic polymer chain>
The acrylic polymer chain contains (meth) acrylic acid alkyl ester as a main constituent monomer component. In the present specification, “(meth) acryl” means acryl and / or methacryl.

  As the (meth) acrylic acid alkyl ester, a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is suitably used. In the (meth) acrylic acid alkyl ester, the alkyl group may have a branch or a cyclic alkyl group.

  Specific examples of (meth) acrylic acid alkyl ester having a chain alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) S-butyl acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, neopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, (Meth) acrylic acid 2-ethylhexyl, (meth) acrylic acid octyl, (meth) acrylic acid isooctyl, (meth) acrylic acid nonyl, (meth) acrylic acid isononyl, (meth) acrylic acid decyl, (meth) acrylic acid isodecyl , Undecyl (meth) acrylate, dodecyl (meth) acrylate, (meth) Isotridodecyl crylate, tetradecyl (meth) acrylate, isotetradecyl (meth) acrylate, pentadecyl (meth) acrylate, cetyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, Specific examples include isooctadecyl (meth) acrylate, nonadecyl (meth) acrylate, aralkyl (meth) acrylate, and the like.

  Specific examples of the (meth) acrylic acid alkyl ester having an alicyclic alkyl group include cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) acrylate, etc. (Meth) acrylic acid cycloalkyl ester; (meth) acrylic acid ester having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth) acrylate; dicyclopentanyl (meth) acrylate, dicyclopentanyloxy Tricycles such as ethyl (meth) acrylate, tricyclopentanyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2-adamantyl (meth) acrylate, 2-ethyl-2-adamantyl (meth) acrylate, etc. (Meth) having the above aliphatic hydrocarbon ring Acrylic acid esters.

  The amount of the (meth) acrylic acid alkyl ester is preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 60% by weight or more based on the total amount of the monomer components constituting the acrylic polymer chain. From the viewpoint of setting the glass transition temperature (Tg) of the polymer chain to an appropriate range, the acrylic polymer chain is an amount of (meth) acrylic acid alkyl ester having a chain alkyl group having 4 to 10 carbon atoms relative to the total amount of the constituent monomer components. Is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 45% by weight or more. In addition, the monomer component which comprises an acryl-type polymer chain removes the urethane (meth) acrylate etc. which become a structural component of a urethane-type segment.

  The acrylic polymer chain may contain a hydroxyl group-containing monomer or a carboxy group-containing monomer as a constituent monomer component. When the acrylic polymer chain has a hydroxyl group-containing monomer as a constituent monomer component, the transparency of the pressure-sensitive adhesive sheet is improved and white turbidity in a high-temperature and high-humidity environment tends to be suppressed.

  Hydroxyl group-containing monomers include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, (meth) acrylic Examples include (meth) acrylic acid esters such as 8-hydroxyoctyl acid, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate and (4-hydroxymethylcyclohexyl) -methyl acrylate. Among these, from the viewpoint of high compatibility with the urethane-based segment and improving the transparency of the pressure-sensitive adhesive sheet, the acrylic polymer chain has a hydroxyalkyl group having 4 to 8 carbon atoms as a constituent monomer component (meth). It is preferable to contain an acrylic ester.

  The amount of the hydroxy group-containing monomer with respect to the total amount of the monomer components constituting the acrylic polymer chain is preferably 1 to 35% by weight, more preferably 3 to 30% by weight, and even more preferably 5 to 25% by weight.

  Carboxy group-containing (meth) acrylic acid esters include acrylic monomers such as (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, croton An acid etc. are mentioned.

  The acrylic polymer chain may contain a nitrogen-containing monomer as a constituent monomer component. Nitrogen-containing monomers include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth) acryloylmorpholine, N-vinyl. Examples thereof include vinyl monomers such as carboxylic acid amides and N-vinylcaprolactam, and cyanoacrylate monomers such as acrylonitrile and methacrylonitrile.

  When the acrylic polymer chain contains a high-polarity monomer such as a hydroxyl group-containing monomer or a carboxy group-containing monomer as a constituent monomer component, the cohesive force of the pressure-sensitive adhesive is increased, and the adhesion retention at high temperatures tends to be improved. is there. On the other hand, when the content of the highly polar monomer is excessively large, the glass transition temperature becomes high, and the adhesiveness and impact resistance at low temperatures may be lowered. Therefore, the amount of highly polar monomer (total of hydroxyl group-containing monomer, carboxy group-containing monomer, and nitrogen-containing monomer) with respect to the total amount of monomer components constituting the acrylic polymer chain is preferably 3 to 40% by weight, and 5 to 35% by weight. More preferred is 10 to 30% by weight. Moreover, 1-25 weight% is preferable, as for the quantity of the nitrogen-containing monomer with respect to the monomer component whole quantity which comprises an acryl-type polymer chain, 2-20 weight% is more preferable, and 3-15 weight% is further more preferable.

  Acrylic polymer chain is a monomer component other than the above, an acid anhydride group-containing monomer, (meth) acrylic acid caprolactone adduct, sulfonic acid group-containing monomer, phosphoric acid group-containing monomer, vinyl acetate, vinyl propionate, styrene, Vinyl monomers such as α-methylstyrene; Cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; Epoxy group-containing monomers such as glycidyl (meth) acrylate; Polyethylene glycol (meth) acrylate, Polypropylene (meth) acrylate Glycol-based acrylic ester monomers such as glycol, (meth) acrylic acid methoxyethylene glycol, (meth) acrylic acid methoxypolypropylene glycol; (meth) acrylic acid tetrahydrofurfuryl, fluorine (meth) acrylate , Silicone (meth) acrylate and (meth) may include acrylic ester monomers such as 2-methoxyethyl acrylate.

  The acrylic polymer chain may contain a polyfunctional monomer or oligomer. The polyfunctional compound contains two or more polymerizable functional groups having an unsaturated double bond such as a (meth) acryloyl group or a vinyl group in one molecule. Polyfunctional compounds include polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, bisphenol A ethylene oxide modified di (meth) acrylate, bisphenol A propylene oxide modified di ( (Meth) acrylate, alkanediol di (meth) acrylate, tricyclodecane dimethanol di (meth) acrylate, ethoxylated isocyanuric acid triacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol di (meth) acrylate, trimethylol Propane tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, ethoxylated pentaerythritol tetra (meth) acrylate , Pentaerythrole tetra (meth) acrylate, dipentaerystol poly (meth) acrylate, dipentaerythrole hexa (meth) acrylate, neopentyl glycol di (meth) acrylate, glycerin di (meth) acrylate, epoxy (meth) Examples include acrylate, butadiene (meth) acrylate, and isoprene (meth) acrylate.

  When the acrylic polymer chain contains a polyfunctional monomer as a constituent monomer component, a branched structure (crosslinked structure) is introduced into the polymer chain. As will be described later, in the pressure-sensitive adhesive of the present invention, a crosslinked structure is introduced into the acrylic polymer chain by the urethane segment. When the introduction amount of the crosslinked structure by the polyfunctional monomer component other than the urethane-based segment is increased, the low-temperature adhesive force of the pressure-sensitive adhesive may be decreased. Therefore, the amount of the polyfunctional compound (excluding urethane acrylate) with respect to the total amount of the monomer components constituting the acrylic polymer chain is preferably 3% by weight or less, more preferably 1% by weight or less, and further preferably 0.5% by weight or less. 0.3 wt% or less is particularly preferable.

The acrylic polymer chain preferably has the highest content of (meth) acrylic acid alkyl ester among the above monomer components. The characteristics of the pressure-sensitive adhesive sheet are easily influenced by the type of monomer (main monomer) having the largest content among the constituent monomers of the acrylic polymer chain. For example, when the main monomer of the acrylic polymer chain is a (meth) acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms, the peak top value of tan δ tends to increase and the impact resistance tends to improve. is there. In particular, when an acrylic acid C ₄ alkyl ester such as butyl acrylate is the main monomer, the peak top value of tan δ tends to increase. The amount of (meth) acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms is preferably from 30 to 80% by weight, more preferably from 35 to 75% by weight, based on the total amount of monomer components constituting the acrylic polymer chain. 40 to 70% by weight is more preferable. In particular, the content of butyl acrylate as a constituent monomer component is preferably in the above range.

The theoretical Tg of the acrylic polymer chain is preferably −50 ° C. or higher. The theoretical Tg of the acrylic polymer chain is preferably −10 ° C. or lower, more preferably −20 ° C. or lower, and further preferably −25 ° C. or lower. Theoretical Tg is a glass transition temperature Tg _i of the homopolymer constituent monomer components of the acrylic polymer chain, the weight fraction W _i of each monomer component, is calculated by the Fox equation below.
1 / Tg = Σ (W _i / Tg _i )

Tg is the glass transition temperature (unit: K) of the polymer chain, W _i is the weight fraction of the monomer component i constituting the segment (copolymerization ratio on a weight basis), and Tg _i is the glass transition temperature of the homopolymer of the monomer component i (Unit: K). As the glass transition temperature of the homopolymer, the values described in Polymer Handbook 3rd edition (John Wiley & Sons, Inc., 1989) can be adopted. The Tg of a homopolymer of a monomer not described in the above document may be a peak top temperature of loss tangent (tan δ) determined by dynamic viscoelasticity measurement.

<Urethane segment>
The urethane-based segment is a molecular chain having a urethane bond, and both ends of the urethane-based segment are covalently bonded to the acrylic polymer chain, whereby a crosslinked structure is introduced into the acrylic polymer chain.

(Structure of urethane segment)
The urethane-based segment is typically obtained by reacting a diol with a diisocyanate and includes a polyurethane chain. From the viewpoint of obtaining a pressure-sensitive adhesive capable of achieving both low-temperature adhesiveness and high-temperature holding power, the molecular weight of the polyurethane chain in the urethane-based segment is preferably 4000 to 50000, more preferably 4500 to 40000, and even more preferably 5000 to 30000.

  The larger the molecular weight of the polyurethane chain in the urethane-based segment, the longer the distance between the crosslinking points of the acrylic polymer chain. When the molecular weight of the polyurethane chain is excessively small and the distance between the crosslinking points is short, the storage elastic modulus increases as the cohesive force increases. Along with this, the viscosity of the pressure-sensitive adhesive sheet decreases and tan δ decreases, so that the step absorbability and impact resistance tend to decrease. When the molecular weight of the polyurethane chain is excessively large and the distance between cross-linking points is long, the storage elastic modulus is small and the adhesion holding force may be insufficient. When the molecular weight of the polyurethane chain is in the above range, since the pressure-sensitive adhesive has appropriate cohesiveness, both impact resistance and adhesion retention can be achieved.

  Examples of the diol used for forming the polyurethane chain include low molecular weight diols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol and hexamethylene glycol; polyester polyol, polyether polyol, polycarbonate polyol, acrylic polyol, epoxy polyol, caprolactone polyol, etc. These are high molecular weight polyols.

  The polyether polyol can be obtained by ring-opening addition polymerization of an alkylene oxide to a polyhydric alcohol. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran. Examples of the polyhydric alcohol include the diols described above, glycerin, trimethylolpropane, and the like.

  The polyester polyol is a polyester having a hydroxyl group at the terminal, and is obtained by reacting a polybasic acid and a polyhydric alcohol so that an alcohol equivalent is excessive with respect to a carboxylic acid equivalent. As the polybasic acid component and the polyhydric alcohol component constituting the polyester polyol, a combination of a dibasic acid and a diol is preferable.

  Dibasic acid components include: aromatic dicarboxylic acids such as orthophthalic acid, isophthalic acid and terephthalic acid; alicyclic rings such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid Dicarboxylic acids of formula; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, octadecanedicarboxylic acid; And dicarboxylic acid anhydrides, lower alcohol esters and the like.

  Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F , Hydrogenated bisphenol A, hydrogenated bisphenol F, and the like.

  As the polycarbonate polyol, a polycarbonate polyol obtained by polycondensation reaction of a diol component and phosgene; a diol component, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, ethyl butyl carbonate, ethylene carbonate, propylene carbonate, carbonic acid Polycarbonate polyols obtained by transesterification with diesters such as diphenyl and dibenzyl carbonate; copolymer polycarbonate polyols obtained by using two or more polyol components in combination; esterification of the above-mentioned various polycarbonate polyols with carboxy group-containing compounds Polycarbonate polyol obtained by reaction; Polycarbonate obtained by etherification reaction between the above-mentioned various polycarbonate polyols and a hydroxyl group-containing compound Bonate polyol; polycarbonate polyol obtained by transesterification of the above-mentioned various polycarbonate polyols with an ester compound; polycarbonate polyol obtained by transesterification of the above-mentioned various polycarbonate polyols with a hydroxyl group-containing compound; the various polycarbonate polyols with dicarboxylic acid compounds Polyester polycarbonate polyols obtained by polycondensation with the above; copolymerized polyether polycarbonate polyols obtained by copolymerizing the above various polycarbonate polyols and alkylene oxides.

  A polyacryl polyol is obtained by copolymerizing a (meth) acrylic acid ester and a monomer component having a hydroxyl group. Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, (meth ) Hydroxyalkyl esters of (meth) acrylic acid such as 4-hydroxybutyl acrylate and 2-hydroxypentyl (meth) acrylate; (meth) acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; N- Examples include methylol (meth) acrylamide. (Meth) acrylic acid esters include methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like.

  The polyacryl polyol may contain a monomer component other than the above as a copolymer component. Other copolymer monomer components include unsaturated monocarboxylic acids such as (meth) acrylic acid; unsaturated dicarboxylic acids such as maleic acid and anhydrides and mono- or diesters thereof; unsaturated nitriles such as (meth) acrylonitrile Unsaturated amides such as (meth) acrylamide and N-methylol (meth) acrylamide; Vinyl esters such as vinyl acetate and vinyl propionate; Vinyl ethers such as methyl vinyl ether; α-olefins such as ethylene and propylene; Examples include halogenated α, β-unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride; α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene.

  The diisocyanate used for forming the polyurethane chain may be either an aromatic diisocyanate or an aliphatic diisocyanate. Aromatic diisocyanates include 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-diphenyldimethylmethane diisocyanate, tetramethyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4- Phenylene diisocyanate, 2-chloro-1,4-phenyl diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl sulfoxide diisocyanate 4,4′-diphenylsulfone diisocyanate, 4,4′-biphenyl diisocyanate, and the like. Aliphatic diisocyanates include butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, isophorone diisocyanate. , Dicyclohexylmethane-4,4′-diisocyanate, 1,3-bis (isocyanatemethyl) cyclohexane, methylcyclohexane diisocyanate and the like.

  As the diisocyanate, a derivative of an isocyanate compound can also be used. Examples of the isocyanate compound derivative include polyisocyanate dimers, isocyanate trimers (isocyanurates), adducts with polymeric MDI and trimethylolpropane, biuret modified products, allophanate modified products, urea modified products, and the like. . As the diisocyanate component, a urethane prepolymer having an isocyanate group at the terminal may be used.

(Introduction of cross-linked structure into acrylic polymer chain by urethane segment)
A compound having a functional group copolymerizable with the monomer component constituting the acrylic polymer chain at the end of the polyurethane chain, or a function capable of reacting with a carboxy group or a hydroxyl group contained in the acrylic polymer chain at the end of the polyurethane chain By using a compound having a group, a crosslinked structure of urethane segments can be introduced into the acrylic polymer chain. Urethane di (meth) having (meth) acryloyl groups at both ends of the urethane chain, since it is easy to introduce cross-linking points uniformly into the acrylic polymer chain and has excellent compatibility between the acrylic polymer chain and the urethane segment. It is preferable to introduce a crosslinked structure with urethane-based segments using acrylate. For example, by crosslinking a monomer component constituting an acrylic polymer chain and urethane di (meth) acrylate, a crosslinked structure of urethane segments can be introduced into the acrylic polymer chain.

  The urethane di (meth) acrylate having (meth) acryloyl groups at both ends is obtained, for example, by using a (meth) acrylic compound having a hydroxyl group in addition to the diol component in the polymerization of polyurethane. From the viewpoint of controlling the chain length (molecular weight) of the urethane-based segment, after reacting diol and diisocyanate so that the isocyanate becomes excessive to synthesize the isocyanate-terminated polyurethane, a (meth) acrylic compound having a hydroxyl group is added. Thus, it is preferable to react the terminal isocyanate group of the polyurethane with the hydroxyl group of the (meth) acrylic compound.

  By reacting the polyhydric alcohol and the polyisocyanate compound so that the polyisocyanate compound becomes excessive, a urethane chain having an isocyanate group at the terminal is obtained. In order to obtain an isocyanate-terminated polyurethane, a diol component and a diisocyanate component are used so that the NCO / OH (equivalent ratio) is preferably 1.1 to 2.0, more preferably 1.15 to 1.5. do it. The diisocyanate component may be added after the diol component and the diisocyanate component are mixed and reacted in substantially equal amounts.

  Examples of the (meth) acrylic compound having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyhexyl (meth) acrylate, hydroxymethylacrylamide, and hydroxyethyl. Examples include acrylamide.

  As urethane (meth) acrylate, using commercial products sold by Arakawa Chemical Industries, Shin-Nakamura Chemical Industry, Toa Gosei, Kyoeisha Chemical, Nippon Kayaku, Nippon Synthetic Chemical Industry, Negami Industrial, Daicel Ornex, etc. Also good. The weight average molecular weight of the urethane (meth) acrylate is preferably 4000 to 50000, more preferably 4500 to 40000, and still more preferably 5000 to 30000.

  The glass transition temperature of urethane (meth) acrylate is preferably 0 ° C. or lower, more preferably −10 ° C. or lower, and further preferably −20 ° C. or lower. By using a low-Tg urethane acrylate, a pressure-sensitive adhesive having excellent low-temperature adhesive strength can be obtained even when a cross-linked structure is introduced by a urethane-based segment to increase the cohesive strength of the base polymer. Although the minimum of the glass transition temperature of urethane (meth) acrylate is not specifically limited, From a viewpoint of obtaining the adhesive which is excellent in high temperature retention, -100 degreeC or more is preferable, -90 degreeC or more is more preferable, and -80 degreeC or more is preferable. Further preferred.

  When a urethane (meth) acrylate is used to introduce a crosslinked structure with a urethane segment into an acrylic polymer chain, the glass transition temperature of the urethane segment of the base polymer is substantially equal to the glass transition temperature of the urethane (meth) acrylate. .

<Preparation of base polymer>
A polymer in which a crosslinked structure of urethane-based segments is introduced into an acrylic polymer chain can be polymerized by various known methods. When urethane (meth) acrylate is used as a constituent component of the urethane-based segment, a monomer component for constituting an acrylic polymer chain and urethane (meth) acrylate may be copolymerized.

  The amount of urethane (meth) acrylate used is preferably 3 to 30 parts by weight and more preferably 4 to 25 parts by weight with respect to 100 parts by weight of the monomer component for constituting the acrylic polymer chain. By adjusting the amount of urethane (meth) acrylate used, it is possible to prepare a base polymer in which the content of the urethane segment is in the above-mentioned range. When the content of the urethane segment is excessively small, the adhesive holding force of the pressure-sensitive adhesive sheet tends to decrease due to a decrease in the cohesiveness of the base polymer. When the content of the urethane segment is excessively large, the viscosity of the pressure-sensitive adhesive sheet decreases as the cohesiveness of the base polymer increases, and the impact resistance tends to decrease.

  Photopolymerization is preferred as a method for polymerizing the base polymer. In the photopolymerization, a polymer can be prepared without using a solvent, and therefore, it is not necessary to dry and remove the solvent when forming the pressure-sensitive adhesive sheet, and a thick pressure-sensitive adhesive sheet can be formed uniformly. Photopolymerization is easy for adjusting the degree of polymerization and can be resumed by re-irradiation with light, and is suitable for forming a semi-cured pressure-sensitive adhesive sheet.

  In the preparation of the base polymer, the monomer component constituting the acrylic polymer chain and the entire amount of urethane (meth) acrylate for introducing the crosslinked structure may be reacted at once, or polymerization may be performed in multiple stages. As a method of performing polymerization in multiple stages, a monofunctional monomer constituting an acrylic polymer chain is polymerized to form a prepolymer composition (preliminary polymerization), and urethane di (meth) acrylate is contained in a syrup of the prepolymer composition. A method of polymerizing (main polymerization) the prepolymer composition and the polyfunctional monomer by adding a polyfunctional compound such as is preferable. The prepolymer composition is a partial polymer containing a polymer having a low polymerization degree and an unreacted monomer.

  By prepolymerizing the constituent components of the acrylic polymer, branch points (crosslinking points) due to a polyfunctional compound such as urethane di (meth) acrylate can be uniformly introduced into the acrylic polymer chain. In addition, a low molecular weight polymer or a mixture of a partially polymerized product and an unpolymerized monomer component (adhesive composition) is applied on a substrate, followed by main polymerization on the substrate to form an adhesive sheet. You can also.

  Since a low polymerization composition such as a prepolymer composition has a low viscosity and excellent coatability, it is a method of performing main polymerization on a substrate after applying a pressure-sensitive adhesive composition that is a mixture of a prepolymer composition and a polyfunctional compound. According to this, the productivity of the pressure-sensitive adhesive sheet can be improved and the thickness of the pressure-sensitive adhesive sheet can be made uniform. Moreover, the semi-hardened adhesive sheet which is excellent in level | step difference absorbability can be formed by adjusting the polymerization rate of this superposition | polymerization.

[Adhesive sheet]
As described above, a prepolymer composition having a low degree of polymerization is prepared by prepolymerization, and a pressure-sensitive adhesive composition obtained by adding a polyfunctional compound or the like to the prepolymer composition is applied in layers on the substrate, By performing polymerization (main polymerization) of the pressure-sensitive adhesive composition, a semi-cured pressure-sensitive adhesive sheet is obtained.

<Preliminary polymerization>
The prepolymer composition can be prepared, for example, by polymerizing a composition in which a monomer component constituting an acrylic polymer chain and a polymerization initiator are mixed. The composition for prepolymer formation may contain a polyfunctional compound (polyfunctional monomer or polyfunctional oligomer). For example, a part of the polyfunctional compound serving as a raw material for the polymer may be contained in the composition for forming a prepolymer, and the remainder of the polyfunctional compound may be added to the main polymerization after polymerization of the prepolymer.

  The prepolymer-forming composition preferably contains a photopolymerization initiator. As the photopolymerization initiator, benzoin ether photopolymerization initiator, acetophenone photopolymerization initiator, α-ketol photopolymerization initiator, aromatic sulfonyl chloride photopolymerization initiator, photoactive oxime photopolymerization initiator, Examples include benzoin photopolymerization initiators, benzyl photopolymerization initiators, benzophenone photopolymerization initiators, ketal photopolymerization initiators, thioxanthone photopolymerization initiators, and acylphosphine oxide photopolymerization initiators.

  In the polymerization, a chain transfer agent, a polymerization inhibitor (polymerization retarder) or the like may be used for the purpose of adjusting the molecular weight. As chain transfer agents, thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, Examples include α-methylstyrene dimer.

  The composition for forming a prepolymer may contain a chain transfer agent or the like as necessary in addition to the monomer and the polymerization initiator. The polymerization initiator and chain transfer agent used for the preliminary polymerization are not particularly limited, and for example, the above-described photopolymerization initiator and chain transfer agent can be used.

  Although the polymerization rate of a prepolymer is not specifically limited, From a viewpoint of setting it as the viscosity suitable for application | coating on a base material, 3 to 50 weight% is preferable and 5 to 40 weight% is more preferable. The polymerization rate of the prepolymer can be adjusted to a desired range by adjusting the type and amount of the photopolymerization initiator, the irradiation intensity / irradiation time of actinic rays such as UV light, and the like.

<Preparation of pressure-sensitive adhesive composition>
Adhesive by mixing urethane (meth) acrylate and, if necessary, the remainder of the monomer component constituting the acrylic polymer chain, a polymerization initiator, a chain transfer agent, other additives, etc. into the prepolymer composition. A composition is prepared. The pressure-sensitive adhesive composition preferably has a viscosity suitable for application on a substrate (for example, about 0.5 to 20 Pa · s). By adjusting the polymerization rate of the prepolymer, the addition amount of urethane (meth) acrylate, the composition of other components (for example, oligomers), the molecular weight, the addition amount, etc., the viscosity of the pressure-sensitive adhesive composition may be in an appropriate range. it can. For the purpose of adjusting the viscosity, a thickening additive or the like may be used.

  The polymerization initiator and chain transfer agent used in the main polymerization are not particularly limited, and for example, the above-described photopolymerization initiator and chain transfer agent can be used. When the prepolymerization initiator remains in the prepolymer composition without being deactivated, the addition of the polymerization initiator for the main polymerization can be omitted.

(Oligomer)
The pressure-sensitive adhesive composition may contain various oligomers for the purpose of adjusting the adhesive strength of the pressure-sensitive adhesive sheet, adjusting the viscosity, and the like. As the oligomer, for example, those having a weight average molecular weight of about 1000 to 30000 are used. As the oligomer, an acrylic oligomer is preferable because of excellent compatibility with the acrylic base polymer.

  The acrylic oligomer contains a (meth) acrylic acid alkyl ester as a main constituent monomer component. Among them, (meth) acrylic acid alkyl ester having a chain alkyl group (chain alkyl (meth) acrylate) and (meth) acrylic acid alkyl ester having an alicyclic alkyl group (alicyclic alkyl) as constituent monomer components Those containing (meth) acrylate) are preferred. Specific examples of the chain alkyl (meth) acrylate and the alicyclic alkyl (meth) acrylate are as exemplified above as the constituent monomers of the acrylic polymer chain.

  The glass transition temperature of the acrylic oligomer is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, and further preferably 40 ° C. or higher. By using a low Tg base polymer into which a cross-linked structure with a urethane-based segment is introduced and a high Tg acrylic oligomer, the adhesive holding force of the pressure-sensitive adhesive sheet tends to be improved. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, but is generally 200 ° C. or lower, preferably 180 ° C. or lower, and more preferably 160 ° C. or lower. The glass transition temperature of the acrylic oligomer is calculated by the aforementioned Fox equation.

  Among the exemplified (meth) acrylic acid alkyl esters, methyl methacrylate is preferable because the chain alkyl (meth) acrylate has a high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth) acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferable. That is, the acrylic oligomer comprises, as constituent monomer components, at least one selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, methyl methacrylate, The thing containing is preferable.

  10-90 weight% is preferable, as for the quantity of alicyclic alkyl (meth) acrylate with respect to the monomer component whole quantity which comprises an acryl-type oligomer, 20-80 weight% is more preferable, and 30-70 weight% is further more preferable. The amount of the chain alkyl (meth) acrylate based on the total amount of the monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and even more preferably 30 to 70% by weight.

  1000-30000 are preferable, as for the weight average molecular weight of an acryl-type oligomer, 1500-10000 are more preferable, and 2000-8000 are more preferable. By using an acrylic oligomer having a molecular weight in this range, the adhesive strength and adhesive retention of the pressure-sensitive adhesive tend to be improved.

  The acrylic oligomer can be obtained by polymerizing the monomer component by various polymerization methods. In the polymerization of the acrylic oligomer, various polymerization initiators may be used. A chain transfer agent may be used for the purpose of adjusting the molecular weight.

  When an oligomer component such as an acrylic oligomer is included in the pressure-sensitive adhesive composition, the content thereof is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight with respect to 100 parts by weight of the base polymer. 2 to 10 parts by weight is more preferable. When the content of the oligomer in the pressure-sensitive adhesive composition is in the above range, the adhesiveness at high temperature and the high temperature holding power tend to be improved.

(Silane coupling agent)
For the purpose of adjusting the adhesive force, a silane coupling agent may be added to the pressure-sensitive adhesive composition. When a silane coupling agent is added to the pressure-sensitive adhesive composition, the addition amount is usually about 0.01 to 5.0 parts by weight with respect to 100 parts by weight of the base polymer, and 0.03 to 2.0 parts by weight. It is preferable that it is a grade.

(Crosslinking agent)
The base polymer may have a crosslinked structure other than the polyfunctional compound as necessary. By including a crosslinking agent in the pressure-sensitive adhesive composition, a crosslinked structure can be introduced into the base polymer. Examples of the crosslinking agent include compounds that react with a functional group such as a hydroxyl group or a carboxy group contained in the polymer. Specific examples of the crosslinking agent include an isocyanate crosslinking agent, an epoxy crosslinking agent, an oxazoline crosslinking agent, an aziridine crosslinking agent, a carbodiimide crosslinking agent, and a metal chelate crosslinking agent.

  When the introduction amount of the crosslinked structure other than the urethane-based segment is increased, the viscosity is lowered and the impact resistance may be lowered. Therefore, the amount of the crosslinking agent used is preferably 3 parts by weight or less, more preferably 2 parts by weight or less, and still more preferably 1 part by weight or less with respect to 100 parts by weight of the base polymer.

(Other additives)
In addition to the components exemplified above, the pressure-sensitive adhesive composition includes a tackifier, a plasticizer, a softener, a deterioration inhibitor, a filler, a colorant, an ultraviolet absorber, an antioxidant, a surfactant, an antistatic agent, and the like. The additive may be included.

<Application of pressure-sensitive adhesive composition and main polymerization>
After the pressure-sensitive adhesive composition is applied in a layer form on the substrate, photocuring is performed by irradiating with actinic rays. When photocuring is performed, a cover sheet is attached to the surface of the coating layer, and actinic rays are irradiated in a state where the pressure-sensitive adhesive composition is sandwiched between two sheets to prevent polymerization inhibition due to oxygen. preferable.

  Arbitrary appropriate base materials are used as a base material and a cover sheet used for formation of an adhesive sheet. The base material and the cover sheet may be a release film having a release layer on the contact surface with the adhesive sheet.

  As the film substrate of the release film, films made of various resin materials are used. Examples of resin materials include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, Examples thereof include polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyarylate resins, polyphenylene sulfide resins, and the like. Among these, polyester resins such as polyethylene terephthalate are particularly preferable. 10-200 micrometers is preferable and, as for the thickness of a film base material, 25-150 micrometers is more preferable. Examples of the release layer material include silicone release agents, fluorine release agents, long-chain alkyl release agents, fatty acid amide release agents, and the like. The thickness of the release layer is generally about 10 to 2000 nm.

  The method of applying the pressure-sensitive adhesive composition on the substrate is roll coat, kiss roll coat, gravure coat, reverse coat, roll brush, spray coat, dip roll coat, bar coat, knife coat, air knife coat, curtain coat. Various methods such as lip coat and die coater are used.

  The main polymerization is carried out by irradiating the pressure-sensitive adhesive composition applied in layers on the substrate with actinic rays. In the main polymerization, an unreacted monomer component in the prepolymer composition reacts with urethane (meth) acrylate to obtain a base polymer in which a crosslinked structure of urethane-based segments is introduced into an acrylic polymer chain. A semi-cured pressure-sensitive adhesive sheet is obtained by adjusting the polymerization rate in the main polymerization and leaving a part of the polymerizable compound unreacted.

The actinic ray may be selected according to the type of polymerizable component such as monomer or urethane (meth) acrylate, the type of photopolymerization initiator, etc., and generally ultraviolet rays and / or short-wavelength visible light is used. . The integrated light quantity of irradiation light is preferably about 100 to 5000 mJ / cm ² . The light source for light irradiation is not particularly limited as long as the photopolymerization initiator contained in the pressure-sensitive adhesive composition can irradiate light in a wavelength range having sensitivity, and the LED light source, high-pressure mercury lamp, ultrahigh-pressure mercury A lamp, a metal halide lamp, a xenon lamp or the like is preferably used. After reaching the predetermined polymerization rate, the polymerization rate can be adjusted to a predetermined range by stopping the light irradiation. As described above, the polymerization rate with the semi-cured adhesive sheet is preferably 90 to 98%.

  By sticking the release films 1 and 2 to the surface of the semi-cured pressure-sensitive adhesive sheet 5, as shown in FIG. 1, a pressure-sensitive adhesive sheet having a release film temporarily attached to both surfaces is obtained. The release film used as a base material or a cover sheet at the time of forming the adhesive sheet may be used as the release films 1 and 2 as they are.

  When the release films 1 and 2 are provided on both surfaces of the pressure-sensitive adhesive sheet 5, the thickness of one release film 1 and the thickness of the other release film 2 may be the same or different. The peeling force when peeling the release film temporarily attached to one surface from the pressure-sensitive adhesive sheet 5 and the peeling force when peeling the release film temporarily attached to the other surface from the pressure-sensitive adhesive sheet 5 are the same. May be different. If the two peel forces are different, the release film 2 (light release film) having a relatively small peel force is peeled off first from the pressure-sensitive adhesive sheet 5 and bonded to the first adherend. In addition, the release film 1 (heavy release film) having a large peeling force is peeled off, and the workability in the case of bonding to the second adherend is excellent.

[Image display device]
The pressure-sensitive adhesive sheet of the present invention can be used for bonding various transparent members and opaque members. The kind of adherend is not particularly limited, and various resin materials, glass, metal and the like can be mentioned. Since the pressure-sensitive adhesive sheet of the present invention has high transparency, it is suitable for bonding optical members such as image display devices. In particular, the pressure-sensitive adhesive sheet of the present invention is suitably used for bonding a transparent member such as a front transparent plate or a touch panel to the viewing-side surface of the image display device because it has excellent step absorbability and impact resistance.

  FIG. 2 is a cross-sectional view showing an example of a laminated configuration of the image display device in which the front transparent plate 7 is bonded to the viewing side surface of the image display panel 10 via the adhesive sheet 5. The image display panel 10 includes a polarizing plate 3 bonded to the surface on the viewing side of an image display cell 6 such as a liquid crystal cell or an organic EL cell via an adhesive sheet 4. The front transparent plate 7 is provided with a printing layer 76 on the periphery of one surface of a transparent flat plate 71. As the transparent plate 71, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate is used. The transparent plate 71 may have a touch panel function. As the touch panel, a touch panel of an arbitrary system such as a resistive film system, a capacitance system, an optical system, and an ultrasonic system is used.

  The polarizing plate 3 provided on the surface of the image display panel 10 and the printed layer 76 forming surface of the front transparent plate 7 are bonded together via the adhesive sheet 5. The order of bonding is not particularly limited, and the bonding of the adhesive sheet 5 to the image display panel 10 may be performed first, or the bonding of the adhesive sheet 5 to the front transparent plate 7 may be performed first. Good. Moreover, both can be bonded simultaneously. From the viewpoint of bonding workability and the like, after peeling one release film (light release film) 2, the exposed surface of the adhesive sheet 5 is bonded to the image display panel 10, and then the other release film 1. It is preferable to peel the (heavy release film) and attach the exposed surface of the pressure-sensitive adhesive sheet to the front transparent plate 7.

  After the pressure-sensitive adhesive sheet 5 and the front transparent plate 7 are bonded together, defoaming is performed to remove the interface between the pressure-sensitive adhesive sheet 5 and the flat plate 71 portion of the front transparent plate 7 and air bubbles in the vicinity of the non-flat portion such as the printed layer 76. Is preferably performed. As the defoaming method, an appropriate method such as heating, pressurization, or reduced pressure can be employed. For example, it is preferable that bonding is performed while suppressing mixing of bubbles under reduced pressure and heating, and then pressurization is performed simultaneously with heating by autoclave treatment or the like for the purpose of suppressing delay bubbles. When defoaming is performed by heating, the heating temperature is generally about 40 to 150 ° C. When pressurization is performed, the pressure is generally about 0.05 MPa to 2 MPa.

  Since the pressure-sensitive adhesive sheet of the present invention has a shear storage elastic modulus in a semi-cured state of 0.15 MPa or less and can easily follow the stepped shape of the printed layer 76 and the like, the generation of voids can be suppressed.

  After the semi-cured adhesive sheet is bonded to an adherend such as a front transparent plate, the adhesive sheet is photocured (post-cured). The polymerization rate increases by post-curing, and accordingly, the storage elastic modulus of the pressure-sensitive adhesive sheet increases, and the adhesion reliability between the pressure-sensitive adhesive sheet 5 and the front transparent member 70 is improved. The polymerization rate of the pressure-sensitive adhesive sheet after post-curing is preferably 99% or more.

  When a gap 90 exists between the housing 9 and the front transparent plate 7, it is preferable to perform sealing by filling the gap 90 with a resin material or the like. As described above, the pressure-sensitive adhesive sheet after post-curing has a high shear storage elastic modulus, and therefore has excellent adhesion reliability in a wide temperature range. Therefore, even when a stress strain occurs at the bonding interface of the pressure-sensitive adhesive sheet due to a temperature change during sealing with a resin material or the like, peeling at the bonding interface can be suppressed. In addition, since the post-cured pressure-sensitive adhesive sheet has a low glass transition temperature and a large peak top value of tan δ, it is excellent in impact resistance in a wide temperature range and hardly peels off due to impact such as dropping.

  As described above, when the pressure-sensitive adhesive sheet is in a semi-cured state containing an unreacted photopolymerizable compound, the shear storage elastic modulus is small and the step absorbability is excellent. Therefore, it is suitably used for bonding to the surface of an image display panel such as a front transparent plate having a printing step or a touch panel.

  Although the explanation was centered on the method of post-curing after bonding with a front transparent plate having a printing step by a printing layer using a semi-curing adhesive sheet, if the step absorbability is not required, the adhesive sheet after complete curing May be bonded to the adherend. For example, a pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive is completely cured is obtained by applying the pressure-sensitive adhesive composition in a layered manner on a substrate and then performing main polymerization so that the polymerization rate is 99% or more. Even when using a fully cured PSA sheet, as with post-curing after bonding using a semi-cured PSA sheet, peeling due to impact such as stress strain or dropping is unlikely to occur and reliability is improved. Excellent adhesion can be realized.

[Optical film with adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention can be used as a film with a pressure-sensitive adhesive in which the pressure-sensitive adhesive sheet is fixed to an optical film or the like in addition to a form in which release films are temporarily attached to both sides as shown in FIG. For example, in the form shown in FIG. 3, the release film 1 is temporarily attached to one surface of the pressure-sensitive adhesive sheet 5, and the polarizing plate 3 is fixed to the other surface of the pressure-sensitive adhesive sheet 5. In the form shown in FIG. 4, an adhesive sheet 4 is further provided on the polarizing plate 3, and the release film 2 is temporarily attached thereon.

  Thus, in the form in which an optical film such as a polarizing plate is previously bonded to the pressure-sensitive adhesive sheet, the release film 1 temporarily attached to the surface of the pressure-sensitive adhesive sheet 5 is peeled off and bonded to the front transparent member. Thereafter, post-curing of the pressure-sensitive adhesive sheet 5 may be performed as necessary.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Production of acrylic oligomer]
60 parts by weight of dicyclopentanyl methacrylate (DCPMA), 40 parts by weight of methyl methacrylate (MMA), 3.5 parts by weight of α-thioglycerol as a chain transfer agent, and 100 parts by weight of toluene as a polymerization solvent are mixed, and nitrogen The mixture was stirred at 70 ° C. for 1 hour under an atmosphere. Next, 0.2 part by weight of 2,2′-azobisisobutyronitrile (AIBN) is added as a thermal polymerization initiator, reacted at 70 ° C. for 2 hours, then heated to 80 ° C. for 2 hours. Reacted. Thereafter, the reaction solution was heated to 130 ° C., and toluene, chain transfer agent, and unreacted monomer were removed by drying to obtain a solid acrylic oligomer. The weight average molecular weight of the acrylic oligomer was 5100.

[Example 1]
(Polypolymerization)
As monomer components for forming the prepolymer, 52.8 parts by weight of butyl acrylate (BA), 10.9 parts by weight of cyclohexyl acrylate (CHA), 9.7 parts by weight of N-vinyl-2-pyrrolidone (NVP), acrylic acid 14.8 parts by weight of 4-hydroxybutyl (4HBA) and 11.8 parts by weight of isostearyl acrylate (ISTA), and a photopolymerization initiator (“Irgacure 184” manufactured by BASF: 0.035 parts by weight, and “ Irgacure 651 ”: After blending 0.035 parts by weight, polymerization is performed by irradiating with ultraviolet rays until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30 ° C.) reaches about 20 Pa · s. A composition (polymerization rate; about 9%) was obtained.

(Preparation of photocurable pressure-sensitive adhesive composition)
In the above prepolymer composition, as a urethane (meth) acrylate, terminal acrylic-modified polyether urethane (“UV-3300B” manufactured by Nippon Synthetic Chemical Industry): 7 parts by weight, and terminal acrylic-modified polyester urethane (manufactured by Nippon Synthetic Chemical Industry) "UV-3010B"): 3 parts by weight, the above acrylic oligomer: 5 parts by weight, as a photopolymerization initiator, Irgacure 184: 0.05 parts by weight, and Irgacure 651: 0.57 parts by weight, as a chain transfer agent, α-methylstyrene dimer (“NOFMER MSD” manufactured by NOF): 0.1 part by weight, and “KBM403” manufactured by Shin-Etsu Chemical Co., Ltd. as a silane coupling agent): To prepare an adhesive composition.

(Preparation of adhesive sheet)
Using the 75 μm thick polyethylene terephthalate (PET) film (“Diafoil MRF75” manufactured by Mitsubishi Chemical Co., Ltd.) with a silicone release layer on the surface as a base material (cumulative release film), the above-mentioned photocurable adhesive is applied on the base material. The agent composition was applied to a thickness of 150 μm to form a coating layer. On this coating layer, a PET film (“Diafoil MRE75” manufactured by Mitsubishi Chemical) having a thickness of 75 μm, on which one side was subjected to silicone release treatment, was bonded as a cover sheet (also a light release film). The laminated body was photocured by irradiating with ultraviolet light for 130 seconds from the cover sheet side with a black light whose position was adjusted so that the irradiation intensity on the irradiation surface immediately below the lamp was 5 mW / cm ² , and the thickness was 150 μm. An adhesive sheet with a rate of 94% was obtained.

[Examples 2-7, Comparative Examples 1-10]
The pre-polymerization monomer composition and the types and amounts of polyfunctional compounds (urethane acrylate and / or polyfunctional acrylate), acrylic oligomer, photopolymerization initiator, and chain transfer agent added to the pressure-sensitive adhesive composition are shown. Changes were made as shown in 1-1 and Table 1-2. Except that, a photocurable pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, and coated on a substrate and photocured to obtain a pressure-sensitive adhesive sheet. In Example 4, Comparative Example 4 and Comparative Example 5, the same pressure-sensitive adhesive composition as in Example 3 was used, and the pressure-sensitive adhesive sheet having the polymerization rate shown in Table 1-1 was obtained by changing the ultraviolet irradiation time. It was.

[Evaluation]
<Weight average molecular weight>
The weight average molecular weight (Mw) of the acrylic oligomer and urethane (meth) acrylate was measured by a GPC (gel permeation chromatography) apparatus (product name “HLC-8120GPC”) manufactured by Tosoh Corporation. As a measurement sample, a filtrate obtained by dissolving a base polymer in tetrahydrofuran to obtain a 0.1 wt% solution was filtered through a 0.45 μm membrane filter. The measurement conditions of GPC are as follows.
(Measurement condition)
Column: G7000HXL + GMHXL + GMHXL, manufactured by Tosoh Corporation
Column size: 7.8 mmφ x 30 cm each (total column length: 90 cm)
Column temperature: 40 ° C., flow rate: 0.8 mL / min
Injection volume: 100 μL
Eluent: Tetrahydrofuran Detector: Differential refractometer (RI)
Standard sample: Polystyrene

<Storage elastic modulus of adhesive sheet, glass transition temperature, and tan δ peak value>
A sample for measurement was prepared by laminating 10 adhesive sheets to a thickness of about 1.5 mm. Using an “Advanced Rheometric Expansion System (ARES)” manufactured by Rheometric Scientific, dynamic viscoelasticity measurement was performed under the following conditions.
(Measurement condition)
Deformation mode: Torsion Measurement frequency: 1Hz
Temperature increase rate: 5 ° C / min Shape: Parallel plate 7.9mmφ

  The shear storage elastic modulus was obtained by reading the storage elastic modulus G ′ at each temperature from the measurement result. The temperature at which the loss tangent (tan δ) becomes maximum (peak top temperature) was defined as the glass transition temperature of the pressure-sensitive adhesive sheet. Further, the value of tan δ (peak top value) at the glass transition temperature was read.

<Adhesive strength>
After peeling off the light release film from the adhesive sheet and pasting together a 50 μm thick PET film and cutting it into a width of 10 mm and a length of 100 mm, the heavy release film is peeled off and pressure bonded to the glass plate with a 5 kg roller. A sample for force measurement was prepared. After holding the sample for measuring the adhesive force in an environment of 25 ° C. or 65 ° C. for 30 minutes, the test piece was peeled off from the glass plate using a tensile tester under the conditions of a tensile speed of 300 mm / min and a peeling angle of 180 °. The peel force was measured.

<Haze>
Using a test piece obtained by bonding an adhesive sheet to non-alkali glass having a thickness of 800 μm (total light transmittance 92%, haze 0.4%), using a haze meter (“HM-150” manufactured by Murakami Color Research Laboratory) Haze was measured. The value obtained by subtracting the non-alkali glass haze (0.4%) from the measured value was defined as the haze of the pressure-sensitive adhesive sheet.

<Step absorbency>
The pressure-sensitive adhesive sheet was cut into a size of 75 mm × 45 mm, the light release film was peeled off from the pressure-sensitive adhesive sheet, and a roll laminator (pressure between rolls: 0.2 MPa, feed rate: at the center of a 125 μm-thick PET film cut out to 100 mm × 50 mm. 100 mm / min). Thereafter, the heavy release film was peeled off, and a 500 μm thick glass plate (100 mm × 50 mm) printed with a black ink with a thickness of 20 μm in a frame shape on a peripheral portion, a roll laminator (inter-roll pressure: 0.2 MPa, feed rate) : 100 mm / min). In the ink printing region of the glass plate, the short side direction was 5 mm from both ends, the long side direction was 15 mm from both ends, and the black ink layer was in contact with the region 5 mm from the four side ends of the adhesive sheet. This sample was treated with an autoclave (50 ° C., 0.5 MPa) for 30 minutes and then observed with a digital microscope having a magnification of 20 times to confirm the presence or absence of bubbles near the boundary of the black ink printing region.

<Peelability from release film>
The pressure-sensitive adhesive sheet is cut into a size of 75 mm × 45 mm, the light release film is peeled off from the pressure-sensitive adhesive sheet, and a 500 μm thick glass plate (100 mm × 50 mm) is formed into a roll laminator (pressure between rolls: 0.2 MPa, feed rate: 100 mm / ). A pickup tape is attached to the end of the heavy release film temporarily attached to the pressure-sensitive adhesive sheet, peeled at a peeling angle of 90 °, and peeled off at the interface between the pressure-sensitive adhesive sheet and the heavy release film. The one peeled off at the interface was defined as NG.

<Interlayer adhesion>
(Preparation of test sample)
The pressure-sensitive adhesive sheet is cut into a size of 75 mm × 45 mm, the light release film is peeled off from the pressure-sensitive adhesive sheet, and a roll laminator (inter-roll pressure: 0.2 MPa, feed rate: 100 mm) at the center of a 500 μm thick glass plate (100 mm × 50 mm). / Min). A 500 μm-thick glass plate (50 mm × 100 mm, the ink printing area is the same as that used in the step absorbency test) by peeling the heavy release film from the pressure-sensitive adhesive sheet and printing black ink with a thickness of 30 μm in a frame shape on the periphery. ) Were bonded together by vacuum pressure bonding (surface pressure 0.3 MPa, pressure 100 Pa). This sample was treated with an autoclave (50 ° C., 0.5 MPa) for 30 minutes, and then cured by irradiating ultraviolet rays with a metal halide lamp (300 mW / cm ² ) from the glass plate side having the black ink printing layer, The polymerization rate was increased to 99%.

  After holding the above sample in an environment of 60 ° C. for 30 minutes, as shown in FIG. 5A, a polystyrene sheet having a thickness of 200 μm was inserted between two glass plates to a distance of 1 mm from the end of the adhesive sheet. Hold for 10 seconds. The edge part of the adhesive sheet was observed with a digital microscope having a magnification of 20 times. A strip-like bubble (see FIG. 5B) or a case where peeling of the pressure-sensitive adhesive sheet from the glass plate occurred was judged as NG, and a case where neither a bubble nor peeling occurred was judged as OK.

<Impact resistance>
A glass plate is bonded to both sides of the pressure-sensitive adhesive sheet in the same manner as the preparation of the sample for the interlayer adhesion test, except that the size of the glass plate not provided with the black ink printing layer is changed to 100 mm × 70 mm. Then, the autoclave and the adhesive were cured to prepare a test sample. As shown in FIG. 6, both ends in the short side direction of the test sample 95 are placed on a table 93 arranged at an interval of 60 mm so that the glass plate 7 provided with the printed layer 76 is on the lower side. The upper surface of the edge part of the glass plate 5 in which the printing layer was not provided was fixed on the stand 80 with the adhesive tape (not shown). The test sample 95 fixed with the adhesive tape on the table 93 is held in an environment of −5 ° C. for 24 hours and then taken out to room temperature within 40 seconds. Was dropped from a height of 300 mm and an impact resistance test was conducted.

  In the impact resistance test, a cylindrical guide 99 is used in order to make the falling position of the metal ball constant, and it is separated from the corner of the inner edge of the frame of the printing region of the printing layer 76 by 10 mm in each of the short side direction and the long side direction. The metal ball 97 was dropped at the position. Two tests were conducted, and in each test, the glass plate that did not peel off was OK, and the glass plate that peeled off in either one or both was judged as NG.

<Physical properties of pressure-sensitive adhesive sheet after curing>
In the preparation of the pressure-sensitive adhesive sheets of each Example and Comparative Example, a pressure-sensitive adhesive sheet having a polymerization rate of 99% was prepared by changing the irradiation time of ultraviolet rays, and viscoelasticity (storage elastic modulus, glass transition temperature) was the same as described above. And tan δ peak), haze and adhesive strength were measured. About Example 4, Comparative example 4 and Comparative example 5, since the composition of the adhesive was the same as that of Example 6, the physical properties of the adhesive sheet after curing were not measured.

[Evaluation results]
The formulation of the pressure-sensitive adhesive composition used for the production of each pressure-sensitive adhesive sheet is shown in Table 1-1 and Table 1-2, and the evaluation results are shown in Table 2-1 and Table 2-2. In Table 1-1 and Table 1-2, each component is described by the following abbreviations.
<Acrylic monomer>
BA: butyl acrylate 2HEA: 2-ethylhexyl acrylate CHA: cyclohexyl acrylate NVP: N-vinyl-2-pyrrolidone 4HBA: 4-hydroxybutyl acrylate 2HEA: 2-hydroxyethyl acrylate ISTA: isostearyl acrylate

<Urethane acrylate>
UV-3300B: “UV-3300B” manufactured by Nippon Synthetic Chemical Industry (polyether urethane diacrylate having a weight average molecular weight of about 12000 and a glass transition temperature of −30 ° C.)
3400: Polyether urethane diacrylate having a weight average molecular weight of about 3400 UA-4200 :: “UA-4200” manufactured by Shin-Nakamura Chemical Co., Ltd. (polyether urethane diacrylate having a weight average molecular weight of about 1000)
UN-350: “Art Resin UN-350” manufactured by Negami Kogyo (polyester urethane diacrylate having a weight average molecular weight of about 12500 and a glass transition temperature of −57 ° C.)
UV-3000B: “UV-3000B” manufactured by Nippon Synthetic Chemical Industry (polyester urethane diacrylate having a weight average molecular weight of about 11000 and a glass transition temperature of −39 ° C.)
UV-3010B: “UV-3010B” manufactured by Nippon Synthetic Chemical Industry (polyester urethane diacrylate having a weight average molecular weight of about 18,000)
Urethane monoacrylate: polyether urethane monoacrylate having a weight average molecular weight of about 1300)
<Multifunctional acrylate>
HDDA: hexanediol diacrylate <photopolymerization initiator>
Irg651: Irgacure 651 (2,2-dimethoxy-1,2-diphenylethane-1-one)
Irg184: Irgacure 184 (1-hydroxy-cyclohexyl-phenyl-ketone)

  In Examples 1 and 2 using a pressure-sensitive adhesive composition obtained by adding urethane diacrylate or the like to a prepolymer composition obtained by prepolymerization of an acrylic monomer having butyl acrylate as a main monomer, a semi-cured pressure-sensitive adhesive sheet However, in the evaluation using the pressure-sensitive adhesive sheet after complete curing, both the interlayer adhesion and the drop impact durability were good.

In Comparative Example 1 using a low molecular weight urethane diacrylate, the adhesive strength of the pressure-sensitive adhesive sheet to the adherend was small before and after photocuring, and the interlayer adhesion and drop impact durability were poor. In Comparative Example 2 in which the amount of urethane diacrylate added was increased, the haze of the pressure-sensitive adhesive sheet was high and the transparency was lowered. Moreover, because of the large G _{'25 ° C.} of the adhesive sheet before curing, it has an inferior step absorbability. In Comparative Example 3 using urethane monoacrylate, the adhesive sheet after photocuring had a low shear storage modulus and poor adhesion durability.

  In Example 3 and Example 5 and Example 6 and Example 7 in which the composition of the acrylic monomer in the prepolymer-forming composition was changed, good adhesive properties were exhibited as in Examples 1 and 2. .

In Example 4 in which the same pressure-sensitive adhesive composition as in Example 3 was used and the polymerization rate was reduced to 92%, the glass transition temperature of the semi-cured pressure-sensitive adhesive sheet was lower than that in Example 3, and accompanying this, G ′ _{25 ° C.} and G ′ _{80 ° C.} were decreased. In Comparative Example 4 in which the polymerization rate was further lowered, the glass transition temperature, G ′ _{25 ° C.} and G ′ _{80 ° C. of} the semi-cured pressure-sensitive adhesive sheet were further lowered, and the adhesive force was insufficient. On the other hand, in Comparative Example 5 in which the polymerization rate was 99%, the step absorbability was insufficient due to an increase in G ′ of _{25 ° C.}

In Comparative Example 6 in which the glass transition temperature was lowered by adjusting the composition of the acrylic monomer without using a urethane-based material, G ′ _{25 ° C.} and G ′ _{80 ° C.} of the pressure-sensitive adhesive sheet after photocuring were small, and adhesion reliability Was inferior. In Comparative Example 7 in which the cohesiveness was increased by increasing the ratio of polar monomers (NVB and 4HBA) in the acrylic monomer component, the adhesion was good, but the impact resistance was reduced due to the high glass transition temperature. Was. A similar tendency was observed in Comparative Example 10.

In Comparative Example 8 in which the ratio of the polyfunctional acrylate in the pressure-sensitive adhesive composition was increased, since the peak top value of tan δ was small and the viscosity was low, the adhesive force was insufficient and the impact resistance was inferior. The same tendency was observed in Comparative Example 9 in which a crosslinked structure was introduced with a low molecular weight urethane diacrylate. In these comparative examples, it is also the main monomer is an acrylic acid C ₄ alkyl esters (butyl acrylate) main monomer of the acrylic polymer chain is an acrylic acid C ₈ alkyl esters (acrylic acid 2-hydroxyethyl) It is considered that tan δ is one of the factors that are smaller than those of Examples 1 to 7.

  From these results, the pressure-sensitive adhesive sheet containing a base polymer in which a crosslinked structure is introduced into an acrylic polymer chain using urethane diacrylate having a predetermined molecular weight exhibits high shear storage modulus even at a low glass transition temperature, and tan δ is Since it is large, it can be seen that both adhesion durability and impact resistance can be achieved.

DESCRIPTION OF SYMBOLS 5 Adhesive sheet 1, 2 Release film 3 Polarizing plate 4 Adhesive sheet 6 Image display cell 10 Image display panel 7 Front transparent plate 9 Case 100 Image display apparatus

Claims (13)

A pressure-sensitive adhesive sheet comprising a base polymer and a photocurable compound and formed into a layer,
Haze is 1% or less,
Adhesive strength to glass is 1.5 N / 10 mm or more,
The shear storage modulus at a temperature of 25 ° C. is 0.15 MPa or less,
A pressure-sensitive adhesive sheet having a glass transition temperature of −3 ° C. or lower and a shear storage modulus at a temperature of 25 ° C. of 0.16 MPa or higher when the pressure-sensitive adhesive composition is cured to a polymerization rate of 99%.   The pressure-sensitive adhesive sheet according to claim 1, wherein a polymerization rate of the pressure-sensitive adhesive composition is 90 to 98%.   The pressure sensitive adhesive sheet according to claim 1 or 2 whose glass transition temperature is -5 ° C or less.   The pressure sensitive adhesive sheet according to claim 1 or 2 whose peak top value of loss tangent is 1.6 or more.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein a peak top value of loss tangent is 1.5 or more when the pressure-sensitive adhesive composition is cured to a polymerization rate of 99%.   The base polymer according to any one of claims 1 to 5, wherein an acrylic polymer chain is cross-linked by a urethane segment, and a content of the urethane segment with respect to 100 parts by weight of the acrylic polymer chain is 3 to 30 parts by weight. The pressure-sensitive adhesive sheet according to claim 1.   The pressure sensitive adhesive sheet according to claim 6 whose weight average molecular weights of said urethane system segment are 4000-50000.   The base polymer is a cross-linked structure of the acrylic polymer chain by the urethane segment by copolymerization of a monomer component constituting the acrylic polymer chain and a urethane (meth) acrylate having a (meth) acryloyl group at the terminal. The pressure-sensitive adhesive sheet according to claim 6 or 7, wherein is introduced. A method of manufacturing an image display device in which a transparent member having a stepped portion is disposed on the viewing side surface,
An image display device that performs photocuring of the pressure-sensitive adhesive sheet by irradiating the pressure-sensitive adhesive sheet with actinic rays after the pressure-sensitive adhesive sheet according to any one of claims 1 to 8 and the transparent member are bonded together. Manufacturing method. It is a manufacturing method of an adhesive sheet given in any 1 paragraph of Claims 1-8,
A composition comprising an acrylic monomer and / or a partially polymerized product thereof and urethane di (meth) acrylate in a layer form on a substrate, and then photocuring by irradiating the composition with actinic rays. Production method.   The said composition is a manufacturing method of the adhesive sheet of Claim 10 whose content of the said urethane (meth) acrylate with respect to a total of 100 weight part of the said acrylic monomer and its partial polymer is 3-30 weight part. .   The manufacturing method of the adhesive sheet of Claim 10 or 11 whose weight average molecular weights of the said urethane di (meth) acrylate are 4000-50000.   The manufacturing method of the adhesive sheet of any one of Claims 10-12 whose glass transition temperature of the said urethane (meth) acrylate is 0 degrees C or less.